1. Field of the Invention
This invention relates to a liquid crystal display element comprising a pair of transparent electrodes consisting of a pair of glass substrates and liquid crystal charged in the space therebetween.
2. Prior Art
For manufacturing LCDs of TN type, the surface of a glass substrate to be used as a transparent electrode is rubbed to impart the liquid crystal molecules an orientation in a given direction. This rubbing orientation process consists of an operation of rubbing the surface of an orientation film coated on the transparent electrode by using a silk cloth. Through this operation, the longitudinal axis of the liquid crystal molecules are orientated in the rubbing direction.
FIG. 3 of the accompanying drawings is a sectional view of a conventional LCD illustrating the structure of its principal area. In this illustration, the reference numerals 1 and 2 respectively denote an upper substrate and a lower substrate. A pair of transparent electrodes 5 and 6 which are made of ITO films respond to display patterns formed on the opposite (inner) surfaces of substrates 1 and 2 which are respectively coated with undercoats 3 and 4. The reference numerals 7 and 8 respectively denote orientation films made of so many thin dielectric films, of which orientation film 7 covers transparent electrode 5 of upper glass substrate 1 while orientation film 8 covers transparent electrode 6 of lower glass substrate 2. The reference numeral 9 designates liquid crystal charged between upper and lower substrates 1 and 2. Arrangement of the crystal molecules contained in the electrode unit can be controlled by rubbing the surface of said orientation films 7 and 8 in a specific direction in advance to charging crystal liquid 9 therebetween. Said undercoats 3 and 4 have the role of preventing sodium compounds in the glass substrates from contaminating crystal liquid 9.
The rubbing orientation operation entails a drawback of generating static electricity on the surface of orientation film 7 and 8 and therefore, when orientation films 7 and 8 are respectively formed directly on the surface of transparent electrodes 5 and 6 as shown in FIG. 3, the static electricity can be discharged into said transparent electrodes 5 and 6 while they are being rubbed. If a considerable amount of static electricity is discharged into the transparent electrodes, it gives rise to generation of heat within the electrodes, eventually leading to partial destruction of the orientation films and hence faulty orientation.
Moreover, since transparent electrodes 5 and 6 and upper and lower substrates 1 and 2 have refractive indices which are different from each other, the contours of transparent electrodes 5 of a LCD having a configuration as shown in FIG. 3 become visible from outside to obstruct the visibility of the proper display of the LCD particularly when no voltage is applied thereto.
Additionally, when orientation films 7 and 8 are formed directly on transparent electrodes 5 and 6, fine electric conductive particles that have been introduced into the LCD cell during manufacturing can destroy the relatively soft orientation films to short-circuit the upper and lower transparent electrodes 5 and 6, a phenomenon which is often referred to as a "touch" between the upper and lower electrodes.